Technical Field
The present invention relates to a manufacturing process in the field of nanotechnology. More particularly, the present invention relates to a process for preparing carbon nanotube membranes that are impregnated with iron oxide. The carbon nanotube membranes prepared by this process are suitable for water desalination and purification applications. Membranes containing iron oxide-impregnated carbon nanotubes and an iron oxide binder and/or matrix are also included in the invention.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Water is the non-substitutional natural resource and most essential substance for all life on earth. Reliable access to clean and affordable water is considered to be one of the most basic humanitarian goals, and remains a major challenge for the 21st century. Good quality water (i.e. pollutant-free water) is not only crucial for human health but also as an essential feedstock for various industries including petrochemicals, oil and gas, food and pharmaceuticals.
Our current water supply faces massive challenges, both old and new. Worldwide, some 780 million people still lack access to safe drinking water (WHO, 2012) [Qu X, Alvarez P J J, Li Q. Applications of nanotechnology in water and wastewater treatment. Water Res 2013. 47: 3931-3946—incorporated herein by reference in its entirety]. Water use has been growing at more than twice the rate of population increase in the last century. As per a report from the United Nations (UN), by 2025, 1800 million people will be facing absolute water scarcity, and two-thirds of the world population could be under stress conditions [Qu X, Alvarez P J J, Li Q. Applications of nanotechnology in water and wastewater treatment. Water Res 2013. 47: 3931-3946; Kar S, Bindal R C, Tewari P K. Carbon nanotube membranes for desalination and water purification: Challenges and opportunities. Nano Today 2012. 7: 385-389—each incorporated herein by reference in its entirety].
Nanotechnology has great potential in wastewater treatment for providing environmentally acceptable water. Nanomaterials have many key physicochemical properties that make them suitable for water treatment. On mass balance they have higher surface area than bulk materials. Thus they are ideal building blocks for developing high capacity sorbents with the ability to be functionalized to enhance their affinity and selectivity.
Various nanostructured materials like zeolites, metal/metal-oxide nanoparticles, dendrimers and carbon nanotubes (CNTs) have been widely employed in water purification. However, carbon nanotubes are considered as a versatile and unique material due to their extraordinary electrical, thermal and mechanical properties. CNTs have been widely employed for the removal of various contaminants from aqueous solutions [Chen C, Hu J, Shao D, Li J, Wang X. Adsorption behavior of multiwall carbonnanotube/iron oxide magnetic composites for Ni(II) and Sr(II). J Hazard Mater 2009. 64:923-928; Di Z C, Li Y H, Laun Z K, Liang J. Adsorption of chromium(VI) ions from water by carbon Nanotubes. Adsorpt Sci Technol 2004. 22:467-474; Wang S G, Gong W X, Liu X W, Yao Y W, Gao B Y, Yue Q Y. Removal of lead(II) from aqueous solution by adsorption onto manganese oxide-coated carbon nanotubes. Sep Purif Technol 2007. 58:17-23—each incorporated herein by reference in its entirety]. Various experimental studies have reported the adsorption of heavy metal ions, small molecules like hydrogen and oxygen, organic chemicals and radionuclides on different CNTs (closed- or open-ended CNTs, single walled or multiwalled) [Li Y H, Ding J, Luan Z, Di Z, Zhu Y, Xu C, Wu D, Wei B. Competitive adsorption of Pb2+, Cu2+ and Cd2+ ions from aqueous solutions by multiwalled carbon nanotubes. Carbon 2003. 4:2787-2792; Chen C, Wang X. Adsorption of Ni(II) from aqueous solution using oxidized multiwall carbon nanotubes. Ind Eng Chem Res 2006. 45:9144-9149; Chen C L, Wang X K, Nagatsu M. Europium adsorption on multiwall carbon nanotube/iron oxide magnetic composite in the presence of polyacrylic acid. Environ Sci Technol 2009. 43:2362-2367; Chen C H, Huang C C. Hydrogen adsorption in defective carbon nanotubes. Sep Purif Technol 2009. 65:305-310; Gaur A, Shim M. Substrate-enhanced O2 adsorption and complexity in the Raman G-band spectra of individual metallic carbon nanotubes. Phys Rev B 2008. 78:1254221-7; Varlot K M, McRae E, Pavlovsky N D. Comparative adsorption of simple molecules on carbon nanotubes dependence of the adsorption properties on the nanotube morphology. Appl Surf Sci 2002. 196: 209-215; Goering J, Kadossov E, Burghaus U. Adsorption kinetics of alcohols on single-wall carbon nanotubes: an ultrahigh vacuum surface chemistry study. J Phys Chem C 2008. 112:10114-10124; Hyung H, Kim J H. Natural organic matter (NOM) adsorption to multi-walled carbon nanotubes: effect of NOM characteristics and water quality parameters. Environ Sci Technol 2008. 42: 4416-4421—each incorporated herein by reference in its entirety].
CNTs have recently attracted considerable attention for synthesis of novel membranes with attractive features for water purification [Iijima S, Ichihashi, T, Ando Y. Pentagons, heptagons and negative curvature in graphite microtubule growth. Nature 1992. 356:776-778; Holt J K, Noy A, Huser T, Eaglesham D, Bakajin O. Fabrication of a carbon Nanotube-embedded silicon nitride membrane for studies of nanometer-scale mass transport. Nano Lett 2004. 4:2245-2250—each incorporated herein by reference in its entirety]. CNTs can also be used as direct filters and effective fillers to improve the membrane performance. CNTs have proven to be excellent filler in membrane due to improved permeability, rejection, disinfection and antifouling behavior. The flux through CNTs has been estimated to be 3-4 orders of magnitude faster than predicted by the Hagen-Poiseuille equation [Li S, Liao G, Liu Z, Pan Y, Wu Q, Weng Y, Zhang X, Yang Z, Tsuid O K C. Enhanced water flux in vertically aligned carbon nanotube arrays and polyethersulfone composite membranes. J Mater Chem A 2014. 2:12171-12176; Majumder M, Chopra N, Andrews R, Hinds B J. Nanoscale hydrodynamics: Enhanced flow in carbon nanotubes. Nature 2005. 438:44; Holt J K, Park H G, Wang Y, Stadermann M, Artyukhin A B, Grigoropoulos C P, Noy A, Bakajin O. Fast Mass Transport Through Sub-2-Nanometer Carbon Nanotubes. Science 2006. 312:1034-1037.—each incorporated herein by reference in its entirety].
In 2004, a well-ordered nanoporous membrane structure comprising an array of aligned CNTs incorporated across a polymer film was introduced [Kar S, Bindal R C, Tewari P K. Carbon nanotube membranes for desalination and water purification: Challenges and opportunities. Nano Today 2012. 7: 385-389; Hinds B J, Chopra N, Andrews R, Gavalas V, Bachas L G. Aligned Multiwalled Carbon Nanotube Membranes. Science 2004; 303:62-65—each incorporated herein by reference in its entirety]. Subsequent to these efforts, a group of researchers studied how fluid moves through nano-sized devices [Holt J K, Park H G, Wang Y, Stadermann M, Artyukhin A B, Grigoropoulos C P, Noy A, Bakajin O. Fast Mass Transport Through Sub-2-Nanometer Carbon Nanotubes. Science 2006. 312:1034-1037—incorporated herein by reference in its entirety]. In the literature, different approaches have been reported by researchers for the synthesis of CNT based membranes. These approaches include but are not limited to:
1. Template-assisted open-ended CNT membranes, in which carbonaceous materials are deposited inside pre-existing ordered porous membranes, e.g anodized alumina [Miller S A, Young V Y, and Martin C R. Electroosmotic Flow in Template-Prepared Carbon Nanotube Membranes. J Am Chem Soc 2001. 123:12335-12342; Chengwei W, Menke L, Shanlin P, Hulin L. Well-aligned carbon nanotube array membrane synthesized in porous alumina template by chemical vapor deposition. Chin Sci Bull 2000. 45:1373-1376—each incorporated herein by reference in its entirety];
2. Aligned-array outer-wall CNT membranes in which the interstices between vertical array of CNT serves as membrane [Srivastava A, Srivastava O N, Talapatra S, Vajtai R, Ajayan P M. Carbon nanotube filters. Nature Materials 2004. 3:610-614—incorporated herein by reference in its entirety];
3. Vertically aligned open-ended CNTs surrounded by an inert polymer or ceramic matrix, or open-ended CNT/polymer composite membranes [Holt J K, Park H G, Wang Y, Stadermann M, Artyukhin A B, Grigoropoulos C P, Noy A, Bakajin O. Fast Mass Transport Through Sub-2-Nanometer Carbon Nanotubes. Science 2006. 312:1034-1037; Hinds B J, Chopra N, Andrews R, Gavalas V, Bachas L G. Aligned Multiwalled Carbon Nanotube Membranes. Science 2004. 303:62-65—each incorporated herein by reference in its entirety];
4. Membranes composed of nanotubes in the form of a thin mat, also known as buckypaper membranes [Pham G T, Park Y B, Wang S, Liang Z, Wang B, Zhang C, Funchess P, Kramer L. Mechanical and electrical properties of polycarbonate nanotube buckypaper composite sheets. Nanotechnology 2008. 19:325705; Dumee L. F, Sears K, Schutz J, Finn N, Huynh C, Hawkins S, Duke M, Gray S. Characterization and evaluation of carbon nanotube Bucky-Papermembranes for direct contact membrane distillation. J Membr Sci 2010. 351:36-43; Cooper S M, Chuang H F, Cinke M, Cruden B A, Meyyappan M. Gas permeability of a buckypaper Membrane. Nano Lett 2003. 3:189-192—each incorporated herein by reference in its entirety].
5. Multistacked membranes of aligned CNT bundles [Andrews R, Jacques D, Rao A M, Derbyshire F, Qian D, Fan X, Dickey E C, Chen J. Continuous production of aligned carbon nanotubes: A step closer to commercial realization. Chem Phys Lett 1999. 303: 467-474—incorporated herein by reference in its entirety];
6. Mixed-matrix membranes, where CNTs are used as fillers in a polymer matrix [Ma Y, Shi F, Wang Z, Wu M, Ma J, Gao C. Preparation and characterization of PSf/clay nanocomposite membranes with PEG 400 as a pore forming additive. Desalination 2012.; 286:131-137; Ebert K, Fritsch D, Koll J, Tjahjawiguna C. Influence of inorganic fillers on the compaction behaviour of porous polymer based membranes. J Membr Sci 2004. 233: 71-78; Majeed S, Fierro D, Buhr K, Wind J, Du B, Fierro A B D, Abetz, V. Multi-walled carbon nanotubes (MWCNTs) mixed polyacrylonitrile (PAN) ultrafiltration membranes. J Membr Sci 2012. 403-404: 101-109; Arockiasamy D L, Alam J, Alhoshan M. Carbon nanotubes-blended poly(phenylene sulfone) membranes for ultrafiltration applications. Appl Water Sci 2013. 3:93-103; Wu H, Tang B, Wu P. Novel ultrafiltration membranes prepared from a multi-walled carbon nanotubes/polymer composite. J Membr Sci 2010. 362:374-383; Shah P, Murthy C N. Studies on the porosity control of MWCNT/polysulfone composite membrane and its effect on metal removal. J Membr Sci 2013. 437:90-98—each incorporated herein by reference in its entirety].
Among the categories above, the mixed-matrix membrane has gained considerable attention due to ease of synthesis and broad applications. Different nanoparticles such as TiO2, Al2O3, ZrO2 and SiO2 can be employed as a filler material for the synthesis of as mixed-matrix membranes with improved performance [Li J B, Zhu J W, Zheng M S. Morphologies and properties of poly(phthalazinone ether sulfone ketone) matrix ultrafiltration membranes with entrapped TiO2 nanoparticles. J Appl Polym Sci 2006. 103:3623-3629; Yang Y, Zhang H, Wang P, Zheng Q, Li J. The influence of nano-sized TiO2 fillers on the morphologies and properties of PSf UF membrane. J Membr Sci 2007. 288:231-238; Cao X, Ma J, Shi X, Ren Z. Effect of TiO2 nanoparticle size on the performance of PVDF membrane. Appl Surf Sci 2006. 253:2003-2010; Oh S J, Kim N, Lee Y T. Preparation and characterization of VDF/TiO2 organic-inorganic composite membranes for fouling resistance improvement. J Membr Sci 2009 345:13-20; Damodar R A, You S J, Chou H H. Study the self-cleaning, antibacterial and photocatalytic properties of TiO2 entrapped PVDF membranes. J Hazard Mater 2009. 172:1321-1328; Wara N M, Francis L F, Velamakanni B. V. Addition of alumina to cellulose acetate Membranes. J Membr Sci 1995. 104:43-49; Yan L, Li Y S, Xiang C B, Xianda S. Effect of nano-sized Al2O3-particle addition on PVDF ultrafiltration membrane performance. J Membr Sci 2006. 276:162-167; Liu F, Abed M R M, Li K. Preparation and characterization of poly(vinylidene fluoride)(PVDF) based ultrafiltration membranes using nano γ-Al2O3. J Membr Sci 2011. 366:97-103; Bottino A, Capannelli G, Comite A. Preparation and characterization of novel porous PVDF-ZrO2 composite membranes. Desalination 2002. 146:35-40; Nunes S P, Peinemann K V, Ohlrogge K, Alpers A, Keller M, Pires A T N. Membranes of poly(ether imide) and nano dispersed silica. J Membr Sci 1999. 157: 219-226—each incorporated herein by reference in its entirety].
Carbon nanotubes (CNTs) are also appealing membrane fillers and act as extraordinary mass transport channels as studied by various research groups. Several studies have shown successful application of CNTs in polymer matrix [Majeed S, Fierro D, Buhr K, Wind J, Du B, Fierro A B D, Abetz, V. Multi-walled carbon nanotubes (MWCNTs) mixed polyacrylonitrile (PAN) ultrafiltration membranes. J Membr Sci 2012.403-404: 101-109; Arockiasamy D L, Alam J, Alhoshan M. Carbon nanotubes-blended poly(phenylene sulfone) membranes for ultrafiltration applications. Appl Water Sci 2013. 3:93-103; Wu H, Tang B, Wu P. Novel ultrafiltration membranes prepared from a multi-walled carbon nanotubes/polymer composite. J Membr Sci 2010.362:374-383; Shah P, Murthy C N. Studies on the porosity control of MWCNT/polysulfone composite membrane and its effect on metal removal. J Membr Sci 2013. 437:90-98—each incorporated herein by reference in its entirety]. Addition of CNTs has been reported to substantially increase the water flux due to hydrophilic surface and large surface pores membranes [Arockiasamy D L, Alam J, Alhoshan M. Carbon nanotubes-blended poly(phenylene sulfone) membranes for ultrafiltration applications. Appl Water Sci 2013. 3:93-103—incorporated herein by reference in its entirety]. Moreover, the tensile strength and fouling resistance of the membranes increased with addition of CNTs.
Given the above, there remains a need for carbon nanotube membranes having low fouling potential, high flux (due to high hydrophilicity and high porosity) and ease of regeneration and cleaning, as well as a simple, low-cost manufacturing process thereof.